Glossary of terms

1080p can be referred to as full HD or full high definition to differentiate it from other HDTV video modes. The term usually assumes a widescreen aspect ratio of 16:9, implying a horizontal resolution of 1920 pixels.

Aberration

The inability of a lens to produce a perfect, sharp image, especially at the edge of the photo.

Accelerator

A specialized hardware or software device to augment the performance of a platform's CPU bus or I/O.

Achromatic

A term which describes a lens system, which is corrected for chromatic aberration.

Addressable resolution

The maximum number of pixels an imaging device is capable of manipulating, and not necessarily the same amount the monitor is capable of displaying.

Additive primaries

Red, green, and blue light when combined produce white light.

Adobe Acrobat

This is software from Adobe that can be used to convert any document into a PDF (Portable Document Format) file. PDF format is cross platform. It can be shared, viewed and printed by anyone who has Adobe’s free Acrobat Reader software.

AD Convertor

In digital cameras the sensor device (CCD/CMOS) outputs an analog signal which is then amplified and processed by an Analog to Digital Converter. Most digital SLR’s have 10 or 12-bit ACD’s which enable them to encode 1024 or 4096 distinct values for the brightness of a single pixel.

Aliasing

Visibly jagged steps along angles, lines, or object edges. Caused by sharp tonal contrast between pixels. In graphic imaging, the undesirable components resulting from the combination of signals or inadequate preparation of signals prior to digitization

Algorithm

A set of mathematical rules for solving a problem in a step-by-step process with a specific beginning and end.

Ambient Light

The available light. Already existing in an indoor or outdoor setting, which is not caused by any illumination created by the photographer.

Angle of view

Angle of view is determined by the focal length of the lens. A wide-angle lens includes more of the scene than a normal (standard lens) or telephoto lens.

Anti-Aliasing

The way a computer can smooth out the jagged edges (aliasing) that bitmap objects reveal on screen or in printouts.

Apochromatic (APO lens)

Lens corrected for chromatic aberrations in all three primary colours. Many manufactures use different names (i.e. NIKON use ED)

APS

The Advanced Photo System (APS) was devised by a group of five manufactures: Canon, Fuji, Kodak, Minolta and Nikon as a 'breakthrough in camera and film technology' and created a new generation of 'point-and-shoot' cameras. Now, with hindsight, regarded as an interim consumer product, which just filled a gap until the more innovative compact digital cameras became affordable. The film size is smaller than 35mm. (see 35mm)

Archive

Long-term offline storage. Current popular media are 8mm magnetic tape and optical discs.

Artifact

A visible defect found in a digital image indicating technical limitations at some stage of the digital process. Compression artifacts can be caused by lossy compression techniques, such as JPEG. And in higher end SLR’s artifacts can be created when using an anti-alias filter. Banding and moiré patterns are also types of artifacts.

ASCII

An acronym for the American Standard Code for information Interchange, which converts keyboard input into digital information. It covers all the printable and control characters.

Aspect ratio

In computer graphics, the images' relationship of width to height must be kept the same when it is displayed on several screens.

Assigning a Profile

Adobe applications use this term for the act of tagging a document with a profile.

Assumed Profile

The profile that acts as the source profile for untagged documents (or ones that the application sees as untagged).

Banding

An artifact of colour gradation in computer imaging when graduated colours break into larger blocks of a single colour, reducing the smooth look of a proper gradation.

Bandwidth

Measurement of a line’s capacity to transmit digital data, usually in megabyte per second.

Batch processing

The performing of a group of computer tasks at the same time.

Bayer Pattern

A Bayer Pattern is a colour filter mosaic, which resembles a three-colour checkerboard, used on single CCD imaging devices to create all the visible colours. The CCD contains one layer of monochromatic photo detectors, with one photo detector per pixel. Each pixel captures one colour, either red, green or blue. A primary colour (GRGB) Bayer Pattern is created by placing two layers of coloured dyes over each other. There are twice as many green filters because the human eye is more sensitive to green, therefore it is important for it to be accurate.

Bezier curve

A mathematically defined curve made up of four points, two ends and two in between, that affect its shape.

Bi-cubic interpolation

A Matrix for comparison of central pixels to surrounding pixels.

BIOS

Basic input/output system. The computer part that manages communications between the computer and peripherals.

Binary Number System

A counting system used by computers to record data, consisting of only 1’s and 0’s.

Binhex

A way in which attachments can be encoded for transmission with e-mail or FTP. Most mail programs can only handle ASCII, so a binhex utility program converts binary programs to ASCII so that people can mail you a binary file.

Bit

A binary digit. The smallest unit of information in a computer, either a 1 or a 0. It can define two conditions (on or off). 8 bits =1 byte.

Bit Depth

Bit depth, also called pixel depth or colour depth, measures how much colour information is available to display or print each pixel in an image. Greater bit depth (more bits of information per pixel) means more available colours and more accurate colour representation in the digital image.

Bitmap

A digitized image that is mapped into a grid of pixels. The colour of each pixel is defined by a specific number of bits.

Black Point

A movable reference point that defines the darkest area in an image, causing all other areas to be adjusted accordingly. It is the density of the darkest black reproducible by a device, such as a printer or a monitor.

Black Point Compensation

A Photoshop setting that ensures that the black point in the source profile is mapped to the black point of the destination profile, and the rest of the tonal range is scaled accordingly.

Blooming

This is a digital capture problem that can occur in very extreme exposures, when there is an overflow of charge from an oversaturated pixel to its neighbour, such as tree leaves shot against a very bright sky. It is typically visible as either a vertical streak or a white halo extending for several pixels. The effect of blooming often increases the visibility of chromatic aberration.

Bokeh

Bokeh describes the rendition of out-of-focus points of light. Differing amounts of spherical aberration alter how lenses render out-of-focus points of light, and thus their bokeh. The word "bokeh" comes from the Japanese word "boke" (pronounced bo-keh) which literally means fuzziness or dizziness.

Bracketing

The technique of taking a number of pictures of the same subject at different levels of exposure. At half and one stop differences, depending on subject and film type.

Buffer

This is RAM storage which temporarily queues images before they’re written to the storage card. It helps to speed up the lag time between shots and gives the ability to shoot in bursts.

Byte

A measurement unit equal to 8 bits of digital information. This is the standard unit in which to measure file size.

Cache

A temporary storage area for information which locates itself between the hard disk and the RAM by employing intuitive logic. It also speeds up the access time of the data.

Calibration

The process of ensuring that all colour production devices (scanners, monitors, printers) conform to a defined standard of colour accuracy by modifying or adjusting their behaviour. Colour calibration is necessary for accurate WYSIWYG colour management.

Candela

The unit of luminous intensity.

CCD

Charge Coupled Device. A light-sensitive microchip, used in scanners and digital cameras as the basis for capturing a digital image.

Channels

Colour information channels are created automatically when you open a new image. The image’s colour mode (not its number of layers) determines the number of colour channels created. For example, an RGB image has four default channels: one for each of the red, green, and blue colours plus a composite channel used for editing the image.

Characterization

The process of determining the output of a system in response to a known input. Characterization provides a way of deriving the colour gamut and reproduction characteristics of a device. Also known as profiling.

Chroma

The visual perception with which an area appears saturated with a particular colour or hue. For example, a red apple is high in chroma; pastel colours are low in chroma; black, white and grey have no chroma. This attribute of colour is used in the colour model L*C*H (Lightness, Chroma, Hue). Chroma is also referred to as saturation.

Chromatic Aberration

This is also known as colour fringing. Colours appear out of register along the edges of high contrast areas, often as red and/or green borders. This is caused by the angle at which light strikes pixels close to the edge of the image area, the sensors respond best when struck by light entering straight into each pixel.

CIE

Commission Internationale d’Eclairage (International Commission on Illumination). An international association of colour scientists that has assembled many of the standards used as the basis for colourimetry.

CIE LAB

Also known as L*a*b. A three-dimensional, mathematical colour model based on human sensitivity to the visual spectrum of light: L = lightness, a = red/green axis of the space, b = blue/yellow axis of the space.

Clipping

By looking at the histogram, you can immediately see whether your scanner has clipped the highlights or shadows. If there is a spike at either end of the histogram, the highlight or shadow values are almost certainly clipped. This means the image information extends beyond the available gamut, resulting in pure black in the shadows or pure white in the highlights.

CMM

Colour Management Module. A CMM is a drop-in component that provides the engine for profile-to-profile conversions. It defines how colours are computed using the sample points in the profiles as guidelines.

CMOS

A Complementary Metal Oxide Semiconductor is a type of image sensor used in some digital cameras. CMOS refers to how a sensor is manufactured, and not to a specific sensor technology.

CMS

Colour Management System. Software dedicated to handling device-to-device conversion of colours. This ensures colour uniformity across input and output devices, by means of calibration and use of device profiles, so that final printed results match originals.

CMYK

Cyan, Magenta, Yellow and Black are the base colours used in printing processes. The four colours of ink used in conventional colour printing. A printing press, applying these inks in varying amounts and overlapping ways, can produce an approximation of most colours.

CMYK Mode

In Photoshop’s CMYK mode, each pixel is assigned a percentage value for each of the process inks. The lightest (highlight) colours are assigned small percentages of process ink colours; the darker (shadow) colours are assigned higher percentages. In CMYK images, pure white is generated when all four components have values of 0%. Use the CMYK mode when preparing an image to be printed using process colours. Converting an RGB image into CMYK creates a colour separation. If you start with an RGB image, it’s best to edit first and then convert to CMYK. In RGB mode, you can use the Proof Setup commands to simulate the effects of a CMYK conversion without changing the actual image data. You can also use CMYK mode to work directly with CMYK images scanned or imported from high-end systems.

A three-colour instrument for measuring light reflected from a surface or transmitted by an object, relating reflectance or transmittance to a mathematical model of human vision. A colourimeter is used for calibration/characterization of monitors and characterization of printers.

Colorimetric Intent

The two rendering intents that try to preserve colourimetry of colours. Colours are mapped to an exact match wherever possible, and where not possible (because the colour is out of gamut), the colour is mapped to its nearest equivalent. Relative colourimetric conversion includes a remapping of the white point so that this colourimetric match is relative to the target white point. Absolute colourimetric converts the colours as if the match were being done relative to the source device’s white point. This is used in some cases, in certain stages of proofing, when the colourimetric match should be absolute.

ColorSync

A colour management system developed by Linotype-Hell. Used on Apple Macintosh computers as a standard for controlling colour throughout the imaging process by using ColorSync ICC profiles for each colour device (monitor, scanner, printer).

Colourant

Something such as a dye or pigment, or phosphors on a monitor, that produces colour on some other medium.

Colour Blotch

Blotchy colour noise.

Colour cast

Overall bias towards one colour in a colour photograph or transparency.

Colour Filter Array

A CFA, made up of very thin layers of coloured dye, is placed over monochrome sensor pixels within digital cameras. The CFA filters out all but the chosen colours for that pixel. During processing, software interpolation produces a full colour for the pixel based on the value of neighbouring pixels. The GRGB Bayer Pattern is the most common CFA used.

Colour Fringing

Also known as chromatic aberration. Colours appear out of register along the edges of high contrast areas, often as red and/or green borders. This is caused by the angle at which light strikes pixels close to the edge of the image area, the sensors respond best when struck by light entering straight into each pixel.

Colour Gamuts

Any color medium representing its own range of color, including film, a monitor, printed images or the human eye.

Colour Separation

The separation of an image into four colour components of CMYK (Cyan, Magenta, Yellow and Black). This allows the image, by the creation of halftone film of each component, to be reproduced in printing.

The three-dimensional range of colour coordinates that mathematically defines the hues and shades a device can print or display.

Colour Temperature

A description of the colour of light in terms of the temperature of the light source, measured in degrees Kelvin. Lower temperatures are redder, higher temperatures are whiter, and the highest are more blue.

Coma

A lens defect, which results in points of light appearing in the image not as points but as discs with comet-like tails.

Continuous Tone

A device that can represent many tonal values for each unit pixel. A monitor is continuous tone as every displayed pixel can represent tone levels by varying the intensities of the red, green and blue light.

Contrast

The relationship between the lightest and darkest areas of an image (D-Min/D-Max).

Conversion

Translating a colour image from the colour space of one device to that of another. Also known as colour transformation.

CPU/ Central Processing Unit

A large chip which holds the "brains" of the computer.

Copyright

A legal property right in an original work of any physical medium of expression, such as photographs. Copyright is more than the right to copy, the owner of copyright holds the exclusive right to reproduce, publicly display, adapt, distribute and to authorize others to do the same.

CRT

Cathode Ray Tube. This is the most common type of computer monitor, consisting of a tube with a source of electrons (a cathode) at one end, and a flattened end coated with phosphors that glow when excited by the electrons.

D50

One of the CIE standard illuminants. D50 is a specification of daylight with a correlated colour temperature of 5000 K.

D65

One of the CIE standard illuminants. D65 is a specification of daylight with a correlated colour temperature of 6500 K. This is the standard white point that is recommended for monitor calibration.

Delta E

The distance in CIE L*a*b* colour space between two colours. Delta E is used to indicate total colour difference and establish quantitative colour tolerances.

Densitometer

A black-and-white or four-colour instrument for reading the amount of light reflected by a surface or transmitted by an object. Reflection densitometers are used to read the density of process-colour inks on press, as well as to calculate other values such as dot gain, ink trap, and hue error. Transmission densitometers are used to read density of black-and-white film.

Density

The degree to which a surface absorbs light. Density is a logarithmic value.

De-skewing

Straightening an image that has been scanned crookedly, or straightening type that is slanted.

Destination Profile

In colour conversion, this is the profile that defines how to convert colours from the profile connection space (PCS) to the target colour space.

Device-Dependent

Describes a colour space that can be defined only by using information on the colour-rendering capabilities of a specific device. For example, RGB is a device-dependent colour model because a specific set of RGB numbers will have a different meaning (produce a different colour) depending on what RGB device is being used.

Device-Independent

Describes a colour space that can be defined using the full gamut of human vision, as defined by a standard observer, independent of the colour-rendering capabilities of any specific device. For example, LAB is device-independent because a specific set of LAB numbers represents the same colour regardless of the device being used.

Distortion

Changing the size of an image in a non-proportional manner. Also known as "anamorphic scaling." Dither - The process of adding dots to a small area in order to smooth out the appearance of an image, or specifying colors to adjacent pixels in order to simulate intermediate colors in a bit mapped image.

Display Profile

Also known as a monitor profile, it’s a profile for a display device such as a computer monitor.

Dithering

A method of simulating gradations or greys or colours by spacing the same coloured dots or pixels at different intervals. For example, dithering can be seen when viewing full colour images on a monitor in 256-colour mode, the illusion of additional colours is created by displaying the 266 primary colours in various dot patterns.

Down-Sampling

The reduction in resolution of an image, necessitating a loss in detail.

D-MAX

The highest level of density.

D-Min

The lowest level of density.

DNG

Digital Negative format. Adobe's publicly available archival format that contains the raw image data and metadata. DNG is an extension of the TIFF 6.0 format and is compatible with the TIFF-EP standard.

DOT

A hafttone dot used in color separations. Haftone dots have fixed density of CMYK, but variable size. By varying the size and shape of a halftone dot, continuous tone colors can be created. Also the minimum addressable point in a dot-matrix printer.

Dot Gain

The growth of halftone dots during print reproduction. The main cause of dot gain is the spreading of ink as it hits paper, but slight dot gain can also be introduced during imaging to film.

DPI

Dots Per Inch. A measurement that indicates the sharpness of screen or print resolution. 72 dpi is good monitor sharpness. 350 dpi produces good printout sharpness.

An image scanning device in which originals are attached to a rotating drum.

Dynamic Range

A range from the brightest white to the darkest dark as measured in density. The dynamic range of measurement devices (such as a scanner or digital camera), describes the distance between the darkest black and the brightest white the device can measure.

Editing Space

A colour space intended specifically for editing colour values. An RGB editing space should ideally be grey-balanced, perceptually uniform and have a gamut large enough to contain the values being edited.

Embedding a Profile

The process of saving a profile in a document file. The profile defines the source profile used when converting the colour values in the file to any other colour space. The embedded profile effectively provides the meanings of the colour numbers in the file.

Ethernet

A networking system providing transfer of data between computer systems and peripherals over a coaxial link.

Effective Pixels

Most digital camera manufacturers use the total number of pixels that a sensor uses as an indication of the camera’s resolution. However the true count is the number of recorded pixels (these are not strictly effective pixels, but that is now a common term and it’s used to represent this number). A sensor measures its pixel count in four ways: total number of pixels, number of read pixels, number of active pixels and recommended recorded pixels. The total CCD pixel count is often what is advertised, but it is the effective pixel count which matters.

Encoding

This term can refer to either 1) a specific set of numerical values within a colour space that can represent a specific colour or 2) the act of assigning specific numerical values to colours.

EPS

Encapsulated PostScript. A standard format for a drawing, image or complete page layout, allowing it to be placed into other documents. EPS files normally include a low-resolution screen preview.

EXIF

The Exchangeable Image File format supports the storage of extended camera information within the header of each file. Such information includes the time and date the image was taken, exposure information and other camera details.

Exposure compensation

To obtain the best results with certain subjects it may be necessary to alter the exposure from the value suggested by the camera. An exposure compensation button [+/-] is now found on most modern auto cameras. Positive compensation may be needed when the main subject is darker than the background and negative compensation may be needed for a subject lighter than the background.

File Size

The digital size of an image, measured in kilobytes (K), megabytes (MB), or gigabytes (GB). File size is proportional to the pixel dimensions of the image. Images with more pixels may produce more detail at a given printed size, but they require more disk space to store and may be slower to edit and print.

Fill Factor

This refers to the percentage of a pixel which is devoted to collecting light.

Focal Length Multiplier

This applies to 35mm lenses used on digital SLR’s that have sensors that are smaller than the normal 35mm negative frame. The multiplier is expressed as a scale factor such as 1.5x. Therefore a digital SLR using a 28mm lens with a multiplier of 1.5x would create the same picture angle as a 42mm lens on a regular 35mm film camera.

Four Thirds

Four Thirds system is a new, open standard facilitating the optimization of the size, performance, and extendibility of digital cameras and lenses. Standardized lens mount allows photographers to freely combine interchangeable lenses and cameras from different manufacturers. The diagonal size of the 4/3 type sensor is about half the size of a 35mm.

FTP

File Transfer Protocol is an Internet service that lets you move files between any two machines on the Internet. To transfer files by FTP you need FTP client software such as Filezilla, SmartFTP, Cyberduck, Transmit, Fetch, Interarchy or WS_FTP, and a connection to the Internet.

Gamma

In CRT display systems, gamma is the relationship between input voltage and output luminance. In colour spaces, it is the mapping of tonal values to perceived brightness. A gamma value of around 2.2 is generally considered perceptually uniform.

Gamut

A gamut is the range of colours that a colour system can display or print. The spectrum of colours seen by the human eye is wider than the gamut available in any colour model.

Gamut Compression

Otherwise known as tonal range compression. The colour space coordinates of a colour space with a larger gamut are reduced to accommodate the smaller gamut of a destination colour space. For example, the gamut of photographic film is compressed for representation in the smaller CMYK gamut used for four-colour process printing.

Gamut Mapping

The remapping of colour and tone values from one colour space to another. If the destination colour space has a smaller gamut, this remapping will require gamut compression.

Generation loss

Photographic duplicates suffer from generation loss; digital data do not suffer loss when copied without processing.

GIGO

Garbage In, Garbage Out.

Gigabyte (Gb)

1,024 megabytes or 1,048,576 kilobytes of digital data.

Gradation

A smooth transition between black and white and from one color to another, or color deficiency.

Gradient

A smooth spread between colors.

Graduated

The process of moving smoothly from one color to another as in vignette.

Grey Balance

The balance between cyan, magenta and yellow colourants required to produce neutral greys without a colour cast. It also can refer to the correction of RGB values in an image so that the greys are neutral.

The 256 distinctly perceptible shades of grey, ranging between white and 100% black, which are capable of being displayed on a computer monitor.

Grid

Regularly spaced horizontal and vertical lines across the picture for accurate positioning when moving elements for compositing.

Halftone

In printing this is the most commonly used method for screening. The visual effect of continuous tones is created by dividing the image into equally spaced halftone cells, each of which is filled with a dot of a known size. The larger dots create the darker tones and the smaller dots create the lighter tones. Black dots are used to recreate black and white images. Cyan, magenta, yellow and black dots are printed at different screen angles to recreate colour images. The four coloured dots form a rosette pattern when correctly registered.

HDR

High Dynamic Range Imaging is a collective term for techniques used to increase the dynamic range of an image. This is often achieved by merging a number of bracketed exposures into a single image.

High-Bit

Anything higher than the minimum 8 bits per channel (256 tone levels). A 16-bit file is a high-bit file.

Highlight

The lightest tone in an image. A spectral highlight is a bright, reflected light source.

Highlight and Shadow Clipping

With a quick look at the histogram, you can immediately see whether or not your scanner has clipped the highlights or shadows. If there’s a spike at either end of the histogram, the highlight or shadow values are almost certainly clipped. We say “almost” because there are some images that really do have a very large number of pure white or solid black areas, but they are pretty rare.

Histogram

A histogram illustrates how pixels in an image are distributed by graphing the number of pixels at each colour intensity level. This can show you whether the image contains enough detail in the shadows (shown in the left part of the histogram), the midtones (shown in the middle), and highlights (shown on the right) to make a good correction. The vertical height of the graph shows how many pixels there are at each brightness level. The histogram also gives a quick picture of the tonal range of the image. An image with full tonal range has a high number of pixels in all areas. Identifying the tonal range helps determine appropriate tonal corrections. Most digital SLR’s feature a histogram review mode, which allows the user to evaluate the exposure and compensate accordingly. If the pixels are situated more toward the left the image may be underexposed, toward the right indicates possible overexposure.

HLS

Hue, Lightness and Saturation is an adaptation of the RGB colour model. When lightness is at maximum, the colour is white.

HSB

Hue, Saturation, and Brightness is also an adaptation of the RGB colour model. It is similar to HLS except that when lightness is at maximum, the colour is at its brightest.

HSV

Hue, Saturation and Value is synonymous with HSB.

Hue

The property of the light from a surface or light source by which we perceive it’s dominant wavelength, or basic colour, such as red, green, purple, etc. Defined by its angular position in a cylindrical colour space, or on a colour wheel.

ICC

The International Colour Consortium is a consortium of colour-related companies that have come together to standardize profile formats and procedures to ensure that programs and operating systems can work together.

ICM

Image Colour Management refers to the implementation of the ICC profile specification in Microsoft Windows.

Image Resolution

The number of pixels displayed per unit of printed length in an image, usually measured in pixels per inch (ppi). In Photoshop, you can change the resolution of an image and the image resolution and pixel dimensions are interdependent. The amount of detail in an image depends on its pixel dimensions; while the image resolution controls how much space the pixels are printed over. For example, you can modify an image’s resolution without changing the actual pixel data in the image-all you change is the printed size of the image. However, if you want to maintain the same output dimensions, changing the image’s resolution requires a change in the total number of pixels.

Image Stabilization

A technology utilizing a 'floating optical element' to compensate for high frequency vibration. On Canon lenses, the 'IS' (Image Stabilization) suffix is used in their names while Nikon uses the 'VR' (Vibration Reduction) suffix in theirs.

Input Profile

A profile for an input device such as a digital camera or scanner.

Interpolation

When an image is re-sampled (increased in size), Photoshop uses an interpolation method to assign colour values to any new pixels based on the colour values of existing pixels in the image. The more sophisticated the method, the more quality and detail from the original image are preserved. Some digital cameras can produce an image larger than the camera’s sensor through interpolation. The more sophisticated the interpolation algorithm is, the less “jaggies” it will create. A technique for increasing the size of a graphic file by creating pixels. Also an extrapolation algorithm. There are two types, sequential and bi-cubic.

IP

Internet Protocol. The computer protocol that allows the Internet to route data from one network to another, until it gets to where it is supposed to go.

IPTC

International Press Telecommunications Council. The IPTC defined a set of metadata attributes that can be applied to images, part of a broader standard developed in the early 1990s and known as the IPTC Information Interchange Model (IIM). Embedded IIM image information is often referred to as an "IPTC header". The Extensible Metadata Platform (XMP) has largely superseded IIM's file structure, but the IIM attributes are defined in the IPTC Core schema for XMP and most image manipulation programs keep the XMP and non-XMP IPTC attributes synchronized. Because of its nearly universal acceptance among photographers — even amateurs — this is by far IPTC's most widely used standard.

The sensitivity of film, or digital camera sensor, to light. Digital cameras have the ability to change ISO sensitivity on the fly. However when you increase the sensitivity to the lighter areas of your image, you often amplify the noise in the darker areas.

A common word used to describe the pixelation of an image, jaggies are a consequence of the square shape of a pixel and are most noticeable at angled lines. Sharpening enhances their visibility.

JPEG

This stands for Joint Photographic Experts Group, and is actually the name of the compression algorithm used by the JPEG format. JPEG is a lossy compression technique supported by JPEG, TIFF, PDF, and PostScript language file formats. JPEG compression provides the best results with continuous-tone images, such as photographs.

JPEG 2000

This is an image coding system that uses compression techniques based on wavelet compression technology. Unlike the standard JPEG format, JPEG 2000 supports optional lossless compression. The advantage is that the wavelet algorithm does not divide the image into blocks when analyzing it for compression the way JPEG does. Instead it analyzes the whole image to get the best compression ratio while maintaining the original quality.

Kelvin

The unit of measurement for colour temperature. The Kelvin scale starts from absolute zero, which is -273 degrees Celsius.

Keyline

A line or boundary that separates areas of different color or tone.

Kilobyte (K)

1,024 bytes of digital data.

Knockout

A masking technique used to separate an element from the background.

Kodak CMS

An application-level Colour Management System developed by Kodak for the Mac OS and Windows 95 and NT.

LAB

Also known as CIELAB, L*A*B*, or Lab colour. It is the device-independent colour space fully supported by Photoshop. The L stands for luminance, while the A and B stand for nothing in particular.

LAN

An acronym for Local Area Network.

Layers

A new image in Photoshop has a single layer. This layer is called the background layer and is analogous to the base layer of a painting. You cannot change the position of the background layer in the stacking order (it is always at the bottom); nor can you apply a blending mode or opacity to a background layer (unless you first convert it to a normal layer). Layers allow you to make changes to an image without altering your original image data. Think of layers as sheets of acetate stacked one on top of the other. Where there is no image on a layer (that is, in places where the layer is transparent), you can see through to the layers below. All layers in a file have the same resolution, start with the same number of channels, and have the same image mode (RGB, CMYK, or Greyscale).

LCD

Liquid Crystal Display. This is the second most common type of computer monitor (the first is CRT), consisting of two layers of polarized plexiglass between which are liquid crystals that change shape in response to electrical currents.

LCH

Luminance, Chroma, Hue. A colour space that is similar to CIELAB, except it uses cylindrical coordinates of lightness, chroma and hue angle instead of rectangular coordinates.

Linearization

A specific type of calibration in which an output device is adjusted to deliver a straight-line relationship between input and output. For example, an imagesetter is linearized to output halftone dot values within a certain tolerance of those input.

Lookup Table

A table that allows input values to be looked up and replaced by corresponding output values.

Lossless

Image and data compression that reduces the file size without data loss.

Lines Per Inch or Lines Per Centimeter. A measurement referring to line screen halftones used in the printing process.

Luminance

The amount of light energy given off by a light source, independent of the response characteristics of the viewer.

LZW

Lemple-Zif-Welch is a lossless compression technique supported by TIFF, PDF, GIF, and PostScript language file formats. This technique is most useful in compressing images that contain large areas of single colour, such as screenshots or simple paint images.

Mask

A temporary stencil restricting the action of various functions to a selected area within the picture or page. Masks can be created by drawing points around an element or automatically by specific density or hue values.

Megabyte (Mb)

1,024 kilobytes or 1,048,576 bytes of digital data.

Metadata

Data embedded and stored within a digital image file. It provides information concerning copyright, credit, restrictions, captions, keywords, or other characteristics. There are several forms of image metadata including EXIF, which is used by digital camera makers and provides large amounts of photo information including the make & model, date & time, aperture and shutter-speed.

Micro Four Thirds

The Micro Four Thirds System Specification (Micro Four Thirds Specification) is an extension of the Four Thirds System Specification for interchangeable-lens type digital camera systems and has been established as a means to enhance the potential for size and weight reduction of the Four Thirds System. The Micro Four Thirds System standard maintains the Four Thirds System concept of "High-picture quality digital-dedicated design," but focuses on reducing overall system thickness and size by aiming for a highly portable compact system.

Midtone

The middle range of tones in an image.

Model Release

A document signed by the subject (if under age, the subject's guardian) to permit the use of their likeness in advertising or commercial photography.

Moiré

A repetitive interface pattern caused by overlapping symmetrical grids of dots or lines that have differing pitch or angle.

Monitor Calibration

The process of setting lookup tables to make the color monitor match output color.

Monitor Profile

Also known as a display profile, it’s the profile for a computer monitor.

Monitor Resolution

The number of pixels or dots displayed per unit of length on the monitor, usually measured in dots per inch (dpi). Monitor resolution depends on the size of the monitor plus its pixel setting. Most new monitors have a resolution of about 96 dpi, while older monitors have a resolution of 72 dpi.

NEF

Nikon's proprietary raw file format.

Noise

Noise is the visible effect of an electronic error or interference in the final image (much like static on the radio). In digital cameras, noise is affected by temperature and ISO sensitivity. Certain colour channels are more affected by noise because the camera sensor is less sensitive to certain colours than others. Many sensors are less sensitive to blue light and therefore compensate by amplifying this channel with more noise. Long exposures can also create a type of noise known as “stuck pixels”, which can appear as fixed coloured dots that are slightly larger than the surrounding pixels.

Noise Reduction

The key to noise reduction is to reduce or eliminate the noise without deteriorating other aspects of the image.

Non-Lossy

Image compression without loss of quality, such as LZW.

Optical Resolution

In the scanning context, this refers to the number of truly separate readings taken from an original within a given distance, as opposed to the subsequent increase in resolution (but not detail) created by software interpolation.

Output Profile

A profile for an output device such as a printer or proofing device.

PCS

Profile Connection Space. The colour space used as the intermediate form for conversions from one profile to another.

PDF

Portable Document File. An electronic snapshot of a document based on the PostScript printing language. PDF is a universal file format that preserves the fonts, images, graphics, and layout of any source document, regardless of the application and platform used to create it. Adobe Acrobat software is commonly used to create PDF’s and Adobe Acrobat Reader is used for viewing them.

Panchromatic Pixels

Pixels that are sensitive to all visible wavelengths. New sensor technology from Kodak builds upon the standard Bayer pattern by adding panchromatic pixels to the RGB pixels present on the sensor. Since no wavelengths of visible light are excluded, these panchromatic pixels allow a (black and white) image to be detected with high sensitivity. The remaining RGB pixels present on the sensor are then used to collect color information, which is combined with the information from the pan pixels to generate the final image.

Perceptual Intent

A rendering intent that tries to preserve the perceptual relationships in an image. This is usually the preferred rendering intent for images that contain many out-of-gamut colours.

Pixel

Derived from the word "Picture elements - the smallest visual unit in a raster file, or a single cell of information. Digital images are composed of touching pixels, each having a specific colour or tone. The eye merges differently coloured pixels into continuous tones.

Pixel Dimensions

The number of pixels along the height and width of a bitmap image. The display size of an image on-screen is determined by the pixel dimensions of the image plus the size and setting of the monitor.

Plug-in

A software module that can be used by Photoshop (and other image editing applications) to provide additional functions including: import of RAW camera files, file format conversions and creative image filters.

Posterization

Stair-stepping of grey levels in distinct visible jumps, as opposed to smooth gradations. Photoshop only gives you 256 possible values for a grey pixel. When you start making dark pixels more different, you eventually make them so different that the image looks splotchy - covered with patches of distinctly different pixels, rather than smooth transitions. This is problem especially with noisy images, because those distinct patches may be noise, not detail. And the posterization is accentuated by sharpening.

Pixels Per Inch or Pixels Per Centimeter. Units of measurement for scanned images which, along with scan dimensions, determine a scan’s resolution and file size.

Printer Resolution

The number of ink dots per inch (dpi) produced by all laser printers, including imagesetters. Most desktop laser printers have a resolution of 600 dpi and imagesetters have a resolution of 1200 dpi or higher.

Pressure sensitive pen

An electronic pen to be used with the digitizing tablet.

Process Colour

The combination of three or more primaries, in various amounts, to simulate the reproduction of full colour.

Profile

A file that contains enough information to let a CMS convert colours into or out of a specific colour space. This may be a device’s colour space, in which case it would be called a device profile with the subcategories of input profile, output profile and display profile. Or it may be an abstract colour space such as a working space (like Adobe RGB 1998).

Profile Mismatch

This happens when you open a file that contains an embedded profile other than the applications assumed profile or working space.

Profile or ICC Profile

Developed by the ICC and introduced in 1995, a profile is a standard file format that communicates measured colour output of a system or device in response to a known input. Its data describes a devices characterization to applications and operating systems that support the format.

Profiling

The act of creating a profile by measuring the current state of the device. Also known as characterization.

Quarter Tones

Tones between shadow and midtones are known as 3/4 tones and those between highlight and midtones are known as 1/4 tones.

RAW Image Format

This is the raw data as it comes directly from the CCD and no in-camera processing is performed, like it is when shooting JPEG or TIFF. The RAW file is thought to be the equivalent of a “digital negative”.

Rendering Intent

The setting that tells the colour management system how to handle the issue of converting colour between colour spaces when going from a larger gamut to a smaller one. The four rendering intents are: perceptual, saturation, relative colourimetric and absolute colourimetric.

Res

A term used to define image resolution instead of ppi. Res 12 indicates 12 pixels per millimeter.

Resampling

An increase or reduction in the number of pixels in an image, required to change its resolution without altering its size.

RGB Mode

Photoshop’s RGB mode uses the RGB model, assigning an intensity value to each pixel ranging from 0 (black) to 255 (white) for each of the RGB components in a colour image. When the values of all three components are equal, the result is a shade of neutral grey. When the value of all components is 255, the result is pure white; when the value is 0, pure black. RGB images use three colours, or channels, to reproduce up to 16.7 million colours on-screen; the three channels translate to 24 (8 x 3) bits of colour information per pixel. (In 16-bit-per-channel images,

RIP

Raster Image Processor. The RIP is either part of a digital printer or a separate computer attached to the printer. The RIP is used to convert the page image from vector form to the raster form needed by the printer.

Sampling

The process of converting analogue data into digital data by taking a series of samples or readings at equal time intervals.

Saturation

The property of the light from a surface or light source by which we perceive the purity of the light. If the light contains many photons of the same wavelength, it is highly saturated. If it contains a mixture of many wavelengths it is less saturated.

Saturation Intent

This is the rendering intent that tries to preserve the saturation properties of colours as much as possible. This is usually the rendering intent preferred for graphics such as graphs or maps where vivid, distinguishable colours are desired.

Screening

This is the method used in printing to simulate different tones and inks by breaking the ink into dots of controlled size and frequency.

Sensor (CCD/CMOS)

The sensor is the chip within a digital camera which records light. The CCD itself is monochrome and requires a colour filter array to produce a coloured image.

Sharpening

Sharpening enhances the visibility of the difference between light and dark tones in an image. Sharpening can be applied in-camera, but it is advisable to shoot digital images in RAW format and apply sharpening in the processing software or using Unsharp Masking in Photoshop.

SIT

A compressed image file format created by StuffIt software.

SMTP

Simple Mail Transfer Protocol. The protocol used for mail transport on the Internet.

Soft-Proofing

Using a monitor as a proofing device to display a simulation of how a document will look when it’s printed.

Source Profile

In a colour conversion, this is the profile that defines how to convert colours from the first colour space to the profile connection space (PCS).

Spectrophotometer

An instrument for reading the spectral properties (reflectance or transmittance) of light across a surface. Spectrophotometric data can be used to calculate densitometric and colourimetric variables.

sRGB

A standard default RGB colour space intended for images on the Internet.

SWOP

Specifications for Web Offset Publication. Printing press standards established to create uniformity of colour reproduction in the printing industry.

Tagging a Document

The act of associating a source profile with a document. You can tag document by either assigning a profile within an application, or by embedding a profile in a document as you save it to a file.

Terabyte TB

1,024 gigabytes or 1,099,511,627,776 bytes.

TCP/IP

Transport Control Protocol and Internet Protocol, which make up a standard guideline for network hardware and software design.

Threshold

The point at which an action begins or changes. The threshold setting used in scanning line art determines which pixels are converted to black and which will become white. The threshold defined in the Unsharp Masking process in Photoshop determines how large a tonal contrast must be before sharpening will be applied to it.

TIFF

Tagged-Image File Format (TIFF) is used to exchange files between applications and computer platforms. TIFF is a flexible bitmap image format supported by virtually all paint, image-editing, and page-layout applications. Also, virtually all desktop scanners can produce TIFF images. TIFF format supports CMYK, RGB, Lab, indexed-colour, and greyscale images with alpha channels and Bitmap-mode images without alpha channels. Photoshop can save layers in a TIFF file; however, if you open the file in another application only the flattened image is visible. Photoshop can also save annotations, transparency, and multi-resolution pyramid data in TIFF format.

Tonal Compression

The remapping of tonal values from a wide dynamic range to a narrower one.

Tonal Range

The tonal range of a digital image is the number of tones it has to describe the dynamic range.

Tone Curves

Also known as gamma curves. These are used to smoothly adjust the overall tonal range of an image, or the individual tonal ranges of each colour channel.

Unsharp Masking

Unsharp masking (USM) is a traditional film compositing technique used to sharpen edges in an image. The Unsharp Mask filter corrects blurring introduced during photographing, scanning, re-sampling, or printing. It is useful for images intended for both print and online viewing. Unsharp Mask locates pixels that differ from surrounding pixels by the threshold you specify and increases the pixels’ contrast by the amount you specify. In addition, you specify the radius of the region to which each pixel is compared. The effects of the Unsharp Mask filter are far more pronounced on-screen than in high-resolution output. If your final destination is print, experiment to determine what settings work best for your image.

Video LUT

The lookup table located in the memory of a video card. The video LUT is accessible by software on the computer, which can use it to convert all the RGB values as they are sent to the monitor. This provides an easy way for software to control the overall gamma and white point characteristics of the video system.

Vignetting

Vignetting causes the corners of an image to appear darker than the centre. This can be caused either by an object such as a lens hood or filter holder entering the field of view, or through the optical characteristics of the lens alone. Using the maximum aperture of a lens will often increase vignetting.

Virtual memory

A system of managing RAM and disk space so that a computer appears to have more memory than it actually does. Data is moved back and forth between the system's memory and disk.

Visual Calibrator

Software used for monitor calibration that requires visual judgments based on targets displayed on the screen, rather than exact measurements using a device.

Wacom

A Paramus, NJ manufacturer of pressure-sensitive stylus and digitizing tablets.

White Balance

Otherwise known as colour balance, white balance refers to the ability to compensate for different colour temperatures associated with light qualities. Human eyes compensate for different lighting conditions, but a digital camera must find the white point in a scene in order to correct the other colours. Most digital cameras are equipped with an auto white balance function and some also have a manual option for balancing under unusual light situations, such as a mix of tungsten and fluorescent.

White Luminance

The luminance of the white point of a monitor.

White Point

The colour and intensity of the brightest white reproducible by a device. In printing, this is the colour and brightness of the paper. On a monitor it is the colour temperature and luminance of the monitor when displaying white, and it can be modified. This term is also used to define the colour of a light source.

WWW

World Wide Web.

WYSIWYG

What you see is what you get. If the way a file appears on your computer monitor exactly matches (in colour, contrast etc.) what you see in an output of the same file, you have achieved the WYSIWYG ideal.

ZIP

The most common compressed file format for PCs.

Zoom

A computer function of focusing down to the element or pixel for editing purposes.